A wireless communication system has been widely developed to provide various kinds of communication services such as voice and data. Generally, the wireless communication system is a multiple access system that can support communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, and a single carrier frequency division multiple access (SC-FDMA) system.
In recent years, due to explosive growth of mobile traffic, evolutionary remedy to coup it will provide a temporary relief to operators. Accordingly, research and industry communities have started to define the next generation systems, broadly known as “5G” communication system. Initially spell-out requirements for 5G are (1) 1000 times higher mobile data volume per area, (2) 10 times to 100 times higher number of connected devices, (3) 10 times to 100 times higher typical user data rate, (4) 10 times longer battery life for low power MMC (Multi-Media Card), and (5) 5 times reduced End-to-End latency.
Some technologies that have been evolved and matured will take key roles again to meet the requirements for 5G. MIMO has drawn a lot of interest because it exploits a new dimension such that spectral efficiency and reliability are enhanced.
Conventional MIMO technique supports two types of operation, such as (1) Closed loop type and (2) Open loop type. In closed mode of operation, the MIMO channel information between a transmitter and a receiver is used to select the weights of pre-coder such that beam-forming gain is achieved. This means if the channel information (e.g., feedback information for the channel or downlink/uplink channel measurement) is not accurate, e.g., due to relative movement of the transmitter and the receiver, the gain from closed-loop operation will be diminished.
In the MIMO system, a number of antenna elements are forced to be limited mainly due to physical dimension it occupies. Limitation in terms of the number of antenna elements are being lifted due to huge benefits we can get if massive MIMO is allowed. For example, extra antennas help by focusing energy into ever smaller regions of space to bring huge improvements in throughput and radiated energy efficiency. In addition, other benefits of massive MIMO include an extensive use of inexpensive low-power components, a reduced latency, a simplification of the medium-access control (MAC) layer, and robustness against intentional jamming.
However, despite of the benefits of the massive MIMO, there still remains to be studied about the allocation of antennas of the massive MIMO and channel coding methods for the massive MIMO.